Areas Covered

Carbohydrates are the body’s preferred source of energy. Carbohydrates are mostly found in plant-based foods, grains, pulses, fruits and vegetables. The body converts carbohydrates into glucose, which provides sufficient energy for your body’s metabolic activity, everyday tasks and physical activity. If the body produces too much glucose, it will be stored in the liver and muscle cells as glycogen, to be used for when the body needs an extra burst of energy. Excess glycogen that cannot be stored in liver and muscle cells is turned into fat. There are two types of carbohydrates Simple (fast release) and Complex (slow release).

Simple carbohydrates (fast release)

Found in processed foods and anything with refined sugar and are easily digested by the body meaning they go straight into the bloodstream supplying a quick release of energy.

Complex carbohydrates (slow release)

Found in nearly all plant-based foods, and usually take longer for the body to digest. They are most commonly found in wholegrain bread, pasta, rice, and vegetables. These are broken down slowly by the digestive system providing a steady release of energy.

The glycemic index (GI)

Glycemic index is a measurement of the type or quality of carbs in a particular food, and how fast 50 grams of this carbohydrate raises blood glucose levels.

Glycemic Index uses a scale of 0 to 100, with higher values given to foods that cause the most rapid rise in blood sugar. Pure glucose serves as a reference point, and is given a GI score of 100.

Glycemic Index values are determined experimentally by feeding human test subjects a fixed portion of the food (after an overnight fast), and subsequently measuring samples of their blood at specific intervals of time.

Glycemic index is a measurement of consuming carbohydrates on their own. It is very rare you do this, remember protein, fats, vegetables and fibre slow down the digestion of carbohydrates. Example: The difference between white and brown rice is the fibrous shell from brown rice has been removed in processing but both rice’s are the same nutrient. Brown rice is high in fibre and white rice is not. Brown rice has a GI of 50 and white rice has a GI of 69. If you eat white rice with a green fibrous vegetable this will make the GI a lot lower.

It is believed that all simple sugars digest quickly and cause a rapid rise in blood sugar, and that the opposite was true for complex carbohydrates”, but that’s not always the case. While many sweet and sugary foods do have high GI’s, some starchy foods like potatoes or white bread score even higher than honey or table sugar (sucrose).

The glycemic load (GL)

Glycemic load GL is a ranking system for carbohydrate content in food portions based on their Glycemic Index (GI) and the portion size.

The usefulness of glycemic load is based on the idea that to some extent, a high glycemic index food consumed over a long period would give the same effect as a low glycemic index food on blood sugar. For example, white rice is very high GI, so eating 50g of white rice at one sitting would give a particular glucose curve in the blood, whilst 25g would give the same curve but half the height. Since the peak height is probably the most important number, multiplying the amount of food by the glycemic index gives an idea of how much effect an actual portion of food has on blood sugar level.

Glycemic load for a single serving of a food can be calculated as the quantity (in grams) of its carbohydrate content, multiplied by its GI, and divided by 100. For example, a 100g slice serving of Watermelon with a GI of 72 and a carbohydrate content of 5g makes the calculation 5 x 0.72=3.6, so the GL is 3.6. A food with a GI of 100 and a carbohydrate content of 10g has a GL of 10 (10 x 1=10), while a food with 100g carbohydrate and a GI of just 10 also has a GL of 10 (100 x 0.1=10).